Double or multiple walled fireplaces and fireplace inserts, in which air is heated between the walls prior to delivery to the room to be heated, are known in the art. For example, Kelley et al U.S. Pat. No. 2,297,776 issued Oct. 6, 1942; Austin U.S. Pat. No. 2,362,526 issued Nov. 14, 1944; Brown U.S. Pat. No. 2,642,859 issued June 23, 1953; Fogel et al U.S. Pat. No. 2,703,566 issued Mar. 8, 1955; Andrews U.S. Pat. No. 3,762,391 issued Oct. 2, 1973; Nelson U.S. Pat. No. 3,965,886 issued June 29, 1976; Nelson U.S. Pat. No. 3,995,611 issued Dec. 7, 1976; Buckner U.S. Pat. No. 4,185,610 issued Jan. 29,1980; Martenson U.S. Pat. No. 4,015,581 issued Apr. 5, 1977; Shaw U.S. Pat. No. 4,059,090 issued Nov. 22, 1977; Jensen U.S. Pat. No. 4,074,679 issued Feb. 21, 1978; Shaw U.S. Pat. No. 4,169,458 issued Oct. 2, 1979 (Canadian Patent No. 1,061,207 issued Aug. 28, 1979); Buckner U.S. Pat. No. 4,185,610 issued Jan. 29, 1980; Wells U.S. Pat. No. 4,254,756 issued Mar. 10, 1981; Hempel U.S. Pat. No. 4,280,473 issued July 28, 1981; Brown Canadian Patent No. 500,427 issued Mar. 2, 1954; Petrescue Canadian Patent No. 1,094,902 issued Feb. 3, 1981; Buckner et al Canadian Patent No. 1,139,624 issued Jan. 18, 1983 all describe various constructions of such double or multiple walled fireplaces. In most of these constructions, convection or fan assisted circulation of room or outside air through the double walls is provided, the air being heated while between the double walls as it passes over the surface of the combustion chamber wall. In certain of these constructions, such as Shaw U.S. Pat. No. 4,059,090, Jensen U.S. Pat. No. 4,074,679, Shaw U.S. Pat. No. 4,169,458 and Wells U.S. Pat. No. 4,254,756, as well as Petrescue Canadian Pat. No. 1,094,902, there is limited control of the flow of alternatively fresh air from outside, or room air, through the double walls and/or the combustion chamber.
Of general background interest are additionally Brooks U.S. Pat. No. 2,359,197 issued Sept. 26, 1944; Bauer U.S. Pat. No. 3,190,282 issued June 22, 1965; and Kamstra et al U.S. Pat. No. 4,143,638 issued Mar. 13, 1979.
It is an object of the present invention to provide an improved and novel construction for controlling the flow of room air and outside air through the air heating chamber between the walls of a double wall fireplace. It is a further object of the present invention to provide a construction for such a fireplace which will, as required, divert flow of some of that air to the combustion chamber.